The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent that it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Fuel injection quantities delivered to an engine are controlled to meet fuel economy requirements and emission standards. The fuel quantity that passes through a fuel injector is determined based on duration of fuel injection (i.e., duration when the fuel injector is energized) given a rail pressure and a flow rate. The rail pressure is determined based on a pressure reading from a pressure sensor when the fuel injection starts. The flow rate is predetermined based on a size of the fuel injectors. The flow rate is assumed to be the same for all injectors along a fuel rail and remains constant during life of fuel injectors.
The fuel injectors along the fuel rail may not deliver the same fuel quantity at the same rail pressure for the same duration of fuel injection. Manufacturing tolerances may lead to differing flow rates across the injectors. Moreover, the actual flow rate may deviate from the predetermined flow rate due to injector coking. “Injector coking” refers to buildup of deposits on the orifice of the injector and is a result of exposing the orifices of the injectors to the high heat of the combustion chamber. Injector coking causes restricted fuel flow and changes the fuel flow rate through the injectors. The fuel flow rate may be constantly changed during life of injectors and may not be changed in the same manner across all of the injectors. As a result, fueling control of the engine may be adversely affected.